1. Field of the Invention
The present invention relates to an X-ray generating tube, and an X-ray generating apparatus and an X-ray imaging system including the X-ray generating tube, which can be used for a medical equipment, a nondestructive inspection apparatus, and the like, for example.
2. Description of the Related Art
In general, an X-ray generating tube accelerates electrons emitted from an electron emitting source with use of a tube voltage in a vacuum and irradiates a target made of a metal such as tungsten with the electron so as to generate X-ray. The tube voltage set in the X-ray generating tube is approximately 100 kV, for example, and the X-ray generating tube is required to have a structure that can withstand the high voltage.
In Japanese Patent Application Laid-Open No. 2009-245806, there is disclosed a technology for stably suppressing breakdown of a valve due to a discharge by applying an electrical resistive film onto an outer surface of the valve as an electrical insulation portion, in which the electrical resistive film is electrically connected to a case main body as an electrical conductive portion of the X-ray tube.
In the X-ray tube disclosed in Japanese Patent Application Laid-Open No. 2009-245806, the electrical resistive film is not applied onto a portion of the valve adjacent to a voltage application portion so as to maintain insulation of the valve. However, in this structure, in order to prevent a potential gradient in an area that is not covered with the electrical resistive film from being steep in a potential distribution on the outer surface of the valve, a complicated valve shape is required.